<template>
  <div class="pagination">
    <button :disabled="pageNo == 1" @click="$emit('getPageNo', pageNo - 1)">上一页</button>
    <button v-if="startNumAndEndNum.start > 1" @click="$emit('getPageNo', 1)" :class="{active: pageNo == 1}">1</button>
    <button v-if="startNumAndEndNum.start > 2" :class="{active: pageNo == 2}">···</button>
    <!-- 中间页部分 -->
    <button
      v-for="(page, index) in startNumAndEndNum.end"
      :key="index"
      v-show="page >= startNumAndEndNum.start"
      @click="$emit('getPageNo', page)"
      :class="{active: pageNo == page}"
    >{{page}}</button>

    <button v-if="startNumAndEndNum.end < totalPage - 1">...</button>
    <!-- <button>···</button> -->
    <button
      v-if="startNumAndEndNum.end < totalPage"
      @click="$emit('getPageNo', totalPage)"
      :class="{active: pageNo == totalPage}"
    >{{totalPage}}
    </button>
    <button :disabled="pageNo == totalPage" @click="$emit('getPageNo', pageNo + 1)">下一页</button>

    <button style="margin-left: 30px">共 {{total}} 条</button>
  </div>
</template>

<script>
export default {
  name: "Pagination",
  props: ['pageNo', 'pageSize', 'total', 'continues'],
  computed: {
    // 总共多少页
    totalPage () {
      // 向上取整
      return Math.ceil(this.total / this.pageSize)
    },
    // 计算出连续的页码的起始数字与结束数字
    startNumAndEndNum () {
      const { continues, pageNo, totalPage } = this
      // 先定义两个变量存储开始数字和结束数字
      let start = 0, end = 0
      // 如果出现不正常的现象也要考虑进去，即如果数据的总页码少于5页的情况下。
      if (continues > totalPage) {
        start = 1
        end = totalPage
      } else {
        // 正常情况下
        start = pageNo - parseInt(continues / 2)
        end = pageNo + parseInt(continues / 2)
        // 如果start计算后出现负数或者0的情况也要考虑进去
        if (start < 1) {
          start = 1
          end = continues
        }
        if (end > totalPage) {
          start = totalPage - continues + 1
          end = totalPage
        }
      }
      return { start, end }
    },
    // sentPageNo(page){
    //   this.$emit('getPageNo', page);
    // }
  }
}
</script>

<style lang="less" scoped>
.pagination {
  text-align: center;
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
</style>